1. Field of the Invention
This invention relates to a semiconductor integrated circuit device and, more particularly, to a semiconductor integrated circuit device having an electrically rewritable nonvolatile semiconductor memory, and a manufacturing method thereof.
2. Description of the Related Art
In an electrically rewritable nonvolatile semiconductor memory device such as a NAND flash memory, a variation in the programming speed caused by a variation in the coupling ratio becomes a problem. Particularly, the problem becomes significant in a multi-value flash memory. The coupling ratio is expressed as follows and is strongly dependent on Cono:Cp=Cono/(Cono+Cox),
where Cono indicates the capacitance between the control gate and the floating gate.
A typical manufacturing method of a NAND flash memory is described in FIGS. 18(a) to (d) of Jpn. Pat. Appln. KOKAI Publication No. 2001-284556, for example.